1. Field of the Invention
The present invention relates to a novel process for producing a thermoelectric material and a novel process for producing a thermoelectric element utilizing it. More particularly, the present invention relates to a process for efficiently producing a thermoelectric material having excellent stability of thermoelectric property and excellent mechanical strength simultaneously by sintering a material powder with hot isostatic pressing, by calcining and then sintering the material powder or by calcining and then sintering the material powder with hot isostatic pressing.
The present invention also relates to a process for producing a thermoelectric element by utilizing the thermoelectric material produced above.
2. Description of the Related Arts
Thermoelectric elements are widely utilized as thermoelectric power generators, temperature sensors, thermoelectric coolers (poltier cooler) and the like. Various kinds of process have been proposed for producing the thermoelectric elements.
For example, a thermoelectric material comprising FeSi.sub.2 and a transition metal was disclosed in Japanese Patent Publication Showa 52-47677. But, this thermoelectric material did not have the satisfactory property.
As another example, a thermoelectric material comprising lead-tellurium compounds and metals of manganese group was disclosed in Laid Open Japanese Patent Application Showa 59-143383. But, this thermoelectric element did not have the satisfactory property either.
In Laid Open Japanese Patent Application Showa 64-37456, a process of sintering solid solution powder of Bi.sub.2 Te.sub.3 -Bi.sub.2 Se.sub.3 was disclosed. But, this process had a problem that it was complicated and not practically advantageous. As a process for solving this problem, a process of copulverizing and mixing, molding and sintering Bi-Sb and Te-Se was disclosed in Laid Open Japanese Patent Application Heisei 2-256283. However, this process had problems that uniformity of the sintered particles between the surface parts and the inner parts was not satisfactory, that stability of the thermoelectric property was not sufficient and that mechanical strength was not good either. Thus, a process for efficiently producing thermoelectric material and elements having excellent stability of thermoelectric property, excellent mechanical property and excellent stability of quality with high productivity has been desired.
Extensive investigations were made by the present inventors with the object of developing a process for efficiently producing a thermoelectric material having the excellent thermoelectric property, mechanical strength and stability of quality and a process for producing a thermoelectric element utilizing it.
And then, it was discovered that the object can be achieved by molding and sintering a material with hot isostatic pressing, by presintering and then sintering the material or by presintering and sintering the material with hot isostatic pressing. The invention was completed on the basis of this discovery.